This invention relates to implantable devices which promote tissue growth or tissue expansion, and more particularly to a novel two-layer tissue expander that can be used for short or long term tissue expansion procedures.
The present invention, although primarily suitable for short term tissue expansion procedures that precede corrective or cosmetic surgery, may also be applied to longer term tissue expansion procedures that generally accompany reconstructive surgery.
Most tissue expanders, whether adapted for long term or short term expansion procedures, are usually made of silicone elastomers. The formation of a tissue expander from silicone can include a molding process as well as a bonding process using adhesives such as RTVs or unvulcanized sheets placed between surfaces to be bonded. The unvulcanized sheets are then baked or cured to complete the bond.
For example, U.S. Pat. No. 4,823,815 to Watson et al. shows a tissue expander device that includes a base layer, an expansion layer and peripheral washers that overlap and extend from the base layer and the expansion layer. The base and expansion layers and the overlapping washers which are formed of silicone are bonded together at their peripheries using RTV adhesives or a vulcanization process wherein unvulcanized sheets are baked or cured to complete the bond. The resulting structure includes an exposed circumferential edge which can lead to tissue trauma, especially if the device is used for long term implantation. In addition, the overlapping washers complicate the structure of the tissue expander and increase the manufacturing cost.
In a short term tissue expansion procedure also known as an intra-operative expansion procedure, a surgeon places a temporary expander in a subcutaneous pocket. The temporary expander is infused or inflated a predetermined amount to place the overlying tissue under tension. After several minutes the tissue expander is deflated and then subsequently reinflated. This expansion and deflation cycle is usually repeated several times during one sitting. When a surgeon has determined that the tissue has stretched sufficiently, the temporary expander is removed and a corrective or reconstructive surgery is performed which may include placement of a permanent implant or tissue expander. If either or both the temporary expander and permanent implant are formed of silicone, then the material costs can be relatively high.
It is thus desirable to provide a tissue expander that need not be vulcanized, baked or cured, can be used for short term or long term tissue expansion procedures, and reduces the prospect of tissue trauma.